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Been developed to measure surface roughness. Among these is the brush surface

analyzer.

1 what is meant by surface finish?

Every machining process leaves its evidence on the machined surface: finely

spaced irregularities left by the cutting tool. Each kind of cutting tools leaves its

own individual pattern, which easily can be identified by the experienced

technician. This pattern is know as surface finish or surface roughness. Every

machined surface is composed of tiny hills and valleys (or bumps and dents).

Whether the surface is result of turning, milling, shaping, grinding, honing, or

polishing can be determined by close investigation. The characteristics of the

surface of a workpiece can meke it unsuitable for some kinds of work.

2. what cause the irregularities in surface of a machined job?

Surface irregularities are related to the efficiency of the machining operation. it is

well known that this efficiency depends, in large measure, upon the correct grindingof the cutting tool-correct clearance, rake, and cutting angel. surface irregularities

are also caused as the chip is forced from the work by the cleaving action of the

cutting tool. The shape of the job can also have a contributing effect for the

vibration of both job and cutting tool leave their mark on the finished surface. Even

the wear on improperly machined ways can be observed in the finish the job. An

efficient grinding job depends largely upon the selection of the correct wheel for the

metal being ground and the proper dressing of the wheel. The quality of the surface

finish is affected by the same factor of proper selection and wheel condition.

3. what factors contribute to the quality of a surface finish?

The most important factors include:

A. The keenness of the tool`s cutting edge.

B. The uniformity of that cutting edge.

C. The smoothness of the tool surface that come in contact with the job, or the

chip during the machining operations.

D. The feeds given by the machine to the cutting tool as it traverses the job.

E. The conditions of the machine ways that guide the cutting tool along its path.

4. what characteristics of surface roughness are measured to obtain an evaluation

of the surface?

Several characteristic contribute to the evaluation of surface quality. These have

been the defined by the American national standards institute ( ANSI ) which

decided to focus on the height, width and direction of surface irregularities.

5. what are the most important characteristics of a surface as defined by ANSI?

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Surface characteristics as defined by ANSI are shown in fig 19-1. The standard

states that these terms and ratings relate to surface produced by such means as

machining,abrading,extruding,custing,molding,forging,roling,coating,planting,blasti

ng or burnishing, etc.

Surface texture. Repetitive or random deviations from the nominal surface whichfrom the pattern of the surface. surface texture includes roughness, waviness, lay,

and flaws.

Surface. The surface of an object the boundary that separates that object from

another object, substance or space.

Nominal surface. Nominal surface is the intended surface contour, the shape and

extent of which is usually shown and dimensioned on a drawing or descriptive

specification.

Measured surface. The measure surface is a representation of the surface obtained

by instrumentation or other means.

Profile. The profile is the contour of a surface in a plane perpendicular to the

surface, unless some other angle is specified.

Nominal profile. The nominal profile is the profile disregarding surface texture.

Measured profile. The measured profile is a representation of the profile obtained by

instrumental or other means.

Center line. The center line is the line which about which roughness is measured; it

is a line parallel to the general direction of the profile within the limits of theroughness-width cutoff, such that the sums of the areas contained between the

center line and those parts of the profile that lie on either side of it are equal.

Micro inch. A micro inch is one millionth of an inch.

(0.000001 in). micro inches may be abbreviated as in.

Roughness. Roughness consists of the finer irregularities in the surface texture,

usually including irregularities that result from the inherent action of the production

process. These are considered to include traverse feed marks and other

irregularities within the limits of the roughness-width cutoff.

Roughness height. For the purpose of this standard, roughness height is rated as

the arithmetical average deviation expressed in micro inches measured normal to

the center line.

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Roughness width. Roughness width is the distance parallel of the nominal surface

between successive peaks of ridges, width constitute the predominate pattern of

the roughness. Roughness width is rated in inches.

Roughness-width cutoff. The greatest spacing of repetitive surface irregularities to

be include in the measurement of average roughness height. Roughness-widthcutoff is rated in inches. Roughness-width cutoff must always be greater than the

roughness width in other to obtain the total roughness height rating.

Waviness. Waviness is the usually widely spaced component of surface texture and

is generally of wider spacing than the roughness-width cutoff. Waviness may result

from such factors as machine or work deflections, vibration, chatter, heat

treatment, or warping strains. Roughness may be considered as superimposed on a

wavy surface. Waviness width. Waviness width is rated in inches as the spacing of

successive wave peaks or successive wave valleys. When specified, the values shall

be maximum.

Lay. The direction of the predominant surface pattern ordinarily determined by the

production method used.

Flaws. flaws are irregularities which occur at one place or at relatively infrequent or

widely varying intervals in a surface. Flaws include such defects as cracks, blow

holes, checks, ridges, scratches, etc. unless otherwise specified, the effects of flaws

shall not be included in the roughness-height measurement.

6. how is the degree of surface roughness measured?

There are occasions when visual comparison with the naked eye will disclose thatone surface is rougher than another. This method is possible only in instances of

wide difference, which could not be misinterpreted by individual reaction. The

methods of evaluating surface roughness used most often are as follow:

*line. The equally spaced vertical lines, Y1, Y2, Y3, etc. (shown fig. 19-6) show the

deviations of the surface from the center line. In order to determine the average,

the parts above the line. The measurement of the height of surface roughness is

determined by the average deviation from the center line.

11. what methods are used to find the average deviation from the center line?

The two method of obtaining the average deviation are :

A. The arithmetical average height.

B. The road-mean-square (rms) average height. The formula of the arithmetical

average height of the surface profile shown in fig. 19-6 follows.

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Average height =

Where n is the total number of vertical measurements.

Rood-mean-square (rsm) average height is about 11 percent higher than the

arithmetical average; this difference is of little importance in most cases. The

formula for the rms average height of the profile shown in fig. 19-6 follow.

Average height =

Where n is the total number of vertical measurements.

The rms average was more commonly used when the tracer method of

measuring surface roughness was in its infancy; arithmetical average is now

considered the standard rating throughout the world.

12. can both the arithmetical average height and the rood-mean-square average

heigt be measured by the same instrument?

The profile meter can measure average roughness in arithmetical average or

rms standards by moving a switch (fig. 19-7)

13. how is it possible to measure the surface finish at the machine where the

work piece is being machined?

No technical knowledge or special skill is needed to operated the instruments

designed for this purpose. A machinist can learn to do this in a few minutes. The

instrument can be set up on a bench or cabinet beside the production machine

and the work piece can be checked at the bench (fig. 19-8), or the tracer can be

used manually on the job while it is in the machine ( fig. 19-9). Work can ak=lso

be checked at on-the-floor inspection units (fig 19-10)

Fig 19-9. Checking surface finish on the machine. (micrometrical manufacturing

Co.)

Fig. 19-10. On-the-floor inspection of surface finish.

14. why are jobs checked for the quality of surface finish during production?

The machinist is always interested in the quality of the finish that is cutting tool

have given to the surface of the machined job. The smoothness and regularity of

the finished surface will indicate:

a. Efficiency of the cutting tool and whether the tool is correctly ground.

b. The approaching breakdown of the cutting edge (or the dulling, loading, and

glazing of the grinding wheel)

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c. The variation in size caused by a change in surface roughness.

d. The need for or the extravagance of additional machining.

By availing himself of a quick, reliable method of checking surface roughness the

machinist saves time and effort.

15. is the profile meter the only instrument used for checking surface finish?

Several instruments are used for checking the quality of surface finish. the brush

surf indicator is well known as a practical shop instrument designed for the

accurate measurement of surface finish roughness. Like the profile meter, the

brush surf indicator (fig. 19-11) measures the irregularities of the surface finish

and records them in micro inches. This is done by means of a tracer stylus,

which registers the rise and fall of the peaks and valleys of the finished surface.

These variations are amplified and indicated on an electrical meter, which is

calibrated to read in micro inches. The surf indicator can be calibrated to read

directly in arithmetical average or root-mean-square average and can be fittedwith various accessories for use in specialized areas.

16. can the quality of the finished surface be observed and measured by optical

instrument?

A machine surface can be observed by means of a microscope, but since surface

roughness must be measured in millionths of an inch a special microscope

technique is necessary for the measurement.